Biomedical subjects
Publications and source records attributed to T Saheki.
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Elasnin, a new human granulocyte elastase inhibitor, produced by the strain of KM-2753 designated as Streptomyces noboritoensis KM--2753 has been isolated from the fermentation broth by column chromatography on silica gel and neutral alumina. Elasnin is a neutral, colorless, and viscous oil (ND17 = 1.4983, [alpha]18D -0.9 degrees, lambdaEtOHmax 291 nm (epsilon, 7,760) having a molecular formula of C24H40O4 (MW 392) as shown by its elemental analysis and mass spectrum. Elasnin markedly inhibits human granulocyte elastase, but it is almost inactive against pancreatic elastase, chymotrypsin, and trypsin. At 1.3 microgram/ml (3.3 X 10(-6) M), elasnin is 50% inhibitory to human elastase, but it causes 50% inhibition of pancreatic elastase at 30.1 microgram/ml (76.8 X 10(-6) M).
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An arabinanase was purified from the culture fluid of Bacillus subtilis F-11. The process was as follows: salting out by (NH4)2SO4, repeated chromatography on hydroxy apatite and gel filtration on Sepharose-6B. The purified enzyme was demonstrated to be homogeneous by disc electrophoresis. The enzyme was found to be active on arabinan and 1,5-arabinan, but inactive on phenyl alpha-L-arabinofuranoside, p-nitrophenyl beta-D-galactopyranoside, arabinoxylan, gum arabic. The enzyme released arabinose, arabinobiose, arabinotriose and higher oligosaccharides during the course of hydrolysis of 1,5-arabinan. The end products were found to be arabinose and arabinobiose after 144 h of hydrolysis.
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Studies on the mechanism and time course of the activation of proteinases A (EC 3.4.23.8), B (EC 3.4.22.9) and C (EC 3.4.12.--) in crude yeast extracts at pH 5.1 and 25 degrees C showed that the increase in proteinase B activity is paralleled with the disappearance of proteinase B inhibitor. Addition of purified proteinase A to fresh crude extracts accelerates the inactivation of the proteinase B inhibitor and the appearance of maximal activities of proteinases B and C. The decrease of proteinase B inhibitor activity and the increase of proteinase B activity are markedly retarded by the addition of pepstatin. Because 10-minus 7 M pepstatin completely inhibits proteinase A without affecting proteinase B activity, this is another indication for the role of proteinase A during the activation of proteinase B. Whereas extracts of yeast grown on minimal medium reached maximal activation of proteinases B and C after 20 h of incubation at pH 5.1 and 25 degrees C, extracts of yeast grown on complete medium had to be incubated for about 100 h. In the latter case, the addition of proteinas A results in maximal activation of proteinases B and C and disappearance of proteinase B inhibitor activity only after 10--20 h of incubation. With the optimal conditions, the maximal activities of proteinases A, B and C, as well as of the proteinase B inhibitor, were determined in crude extracts of yeast that had been grown batchwise for different lengths of time either on minimal or on complete medium. Upon incubation, all three proteinases were activated by several times their initial activity. This reflects the existence of proteolytically degradable inhibitors of the three proteinases and together with the above mentioned observations it demonstrates that the "activation" of yeast proteinases A, B and C upon incubation results from the proteolytic digestion of inhibitors rather than from activation of inactive zymogens by limited proteolysis.
Urea synthesis was studied using the isolated liver perfusion with ammonium cholride and glutamine as nitrogen sources. The rate of urea formation increases with ammonium cholorde concentration up to 5mM, and the rate remained constant in the range between 5 and 20mM of ammonium chloride as the substrate. The concentration of ammonia in the medium to support the half-maximum velocity of urea formation was 0.7mM. The rate of urea formation was stimulated by the addition of 2.5mM ornithine, and the greater part of the ornithine which was taken up into the liver was accumulated as citrulline in the presence of ammonia. A considerable accelerating effect of N-acetylglutamate on the synthetic rate was observed, but a rather high concentration of N-acetylglutamate was required in order to obtain the maximum effect possibly, because its permeability into liver cells may be limited. A marked additive effect on the rate of urea formation was observed with the combined addition of ornithine and N-acetylglutamate. The metabolic conversion of glutamine nitrogen to urea in the perfused rat liver and the effect of several compounds which stimulated urea synthesis with ammonia were further examined. The process of conversion of glutamine nitrogen to urea might be composed of the following three steps. In the first lag phase, a small amount of glutamine was removed from the medium. In the second stage, the glutamine level decreased rapidly and ammonia was accumulated in the perfusate. The third stage was a period in which glutamine concentration remained at a constant low level, and the accumulated ammonia was rapidly conversed to urea. The rate of urea formation in this third stage was found to be much higher than that with ammonia as the substrate. The maximum rate of glutamine removal was obtained at pH 7.7 of the perfusate and at a concentration of 10mM glutamine. Urea formation with glutamine was also stimulated by the addition of ornithine, malate, or N-acetylglutamate, which had accelerating effects on the urea synthesis with ammonia. This stimulation was due to an effective conversion of ammonia to urea, but no change in the rate of removal glutamine was obtained.
Capacities for urea synthesis and amino acid patterns in the perfused livers isolated from rats fed low and high-protein diets were compared. Urea formation with amjonium chlorode as the nitrogen source in perfused livers isolated from rats fed on a 70% casein diet was rapid and the efficiency of conversion of ammonia to urea was 97.9%. However, that in livers isolated from rats fed on a 5% casein diet was much slower and the efficiency of conversion of ammonia to urea was only 36.1%. The ratios of the rate of urea formation from ammonium chloride to activity of ornithine transcarbamylase [EC 2.1.3.3.] in the perfused livers of rats fed on 5 and 70% casein diets were calculated. The ratio of the former condition was much lower than that of the latter. The ratios reached nearly the same level by the addition of ornithine and N-acetylglutamate, the addition of which to the perfusate caused marked elevation of the ratios in both cases. In the perfused livers from rats fed on a 5% casein diet a considerable portion of the ammonia added to the perfusate was fixed into an amino ro an amide group of amino acids such as alamin, aspartate, and glutamine. On the other hand, in the perfused livers from rats fed on a 70% casein diet most of the ammonia added was converted to urea. The regulation of urea synthesis and the relation between anabolism and catabolism of amino acids in rat livers subjected to different dietary conditions were compared.
Sephadex G-100 gel filtration of a purified mixture of tryptophan-synthase-inactivating enzymes I and II from Saccharomyces cerevisiae, which had previously been identified as yeast proteinases A and B, yields two coincident peaks of tryptophan-synthase-inactivating activity and proteinase A and B activities. The peaks correspond to molecular weights of approximately 100 000 and 50 000. It could be demonstrated, with purified proteinases A and B, that the high molecular weight peaks is due to the formation of a stoichiometric complex between proteinases A and B. The AB complex can easily be separated into its constituent enzymes by DEAE-Sephadex chromatography. When in the AB complex, proteinase B molecules still bind the specific proteinase B inhibitor from yeast.
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Argininosuccinate synthetase (ASS) is a urea cycle enzyme with a tetrameric structure composed of identical subunits. Citrullinemia is an autosomal recessive disease caused by a deficiency of ASS. We have previously identified 20 mutations in ASS mRNA of human classical citrullinemia. However, it is difficult to evaluate the effects of each mutation on the enzyme structure and function, since most of the patients are compound heterozygotes. In the present study, wild-type ASS and 12 mutant ASSs were expressed with a bacterial expression system and analyzed enzymologically and immunochemically. The properties of the purified recombinant protein with wild-type human ASS showed good agreement with native enzyme purified from human liver. Mutant ASS proteins with an expected molecular mass, except for delta 7b/Ex16, were highly expressed in the bacterial cells. It was difficult to extract ASS proteins with some mutations (A118T, delta Ex7, R157H, R363W, R363L, G390R and ins37b/Ex15&16) from cells by freezing and thawing. Extractable mutant proteins were as follows: G280R mutant was extracted with an amount of ASS protein similar to wild-type but with no ASS activity, and A192V, R272C and R304W mutants detected various amounts of ASS protein (13, 110 and 33% of wild-type, respectively) with a low ASS activity and abnormal kinetics. Higher Km values for citrulline were obtained in mutant ASSs with A192V (15 mmol/1), R272C (4.2 mmol/l) and R304W. (190 mmol/l) than in wild-type ASS (0.056 mmol/l). The results confirm that these mutations are responsible for ASS deficiency and also indicate that these amino acid residues are important for the function and structure of ASS protein.